The present invention relates to an apparatus and method for manufacturing blow molded plastic articles and particularly to manufacturing articles without the need for typical blow molding presses or clamping systems.
It is well-known that blow molding is effective in fabricating hollow plastic articles. Typically when molding articles in a blow molding process, a parison is extruded and the parison is accommodated in a suitable cavity in one-half of a blow mold. The more complex the shape of the article, the more complex will be the shape of the mold and the cavity in the mold. For very simple articles, the parison may be extruded to hang vertically and the mold halves may be closed around the parison moving in a horizontal direction. For other slightly more complex parts, particularly larger parts, it may be desirable to place the parison in the mold as the parison is being extruded. When the parison has been accommodated in the lower mold half, the lower mold half is then often moved in a substantially horizontal direction to a molding station. When the lower mold half, accommodating the parison, is in the molding station, a molding press is then used to move the upper mold toward the lower mold half to close the mold prior to blow molding. Substantial force is required in the blow molding press as, in many cases, the press is required to pinch the parison at either end and the resultant flow of plastic material must be accommodated by the press forces, while at the same time the press must close to bring the mating surfaces of the mold halves together. This is required so that the parison does not expand into any space between the mating surfaces of the mold halves during the blowing operation. The press is also required to withstand whatever pressures may be exerted on the mold halves tending to separate them, arising from the pressure of the blowing gas operating over the area of the mold cavity.
The prior art offers several solutions for placing a molten parison in what are usually lower mold halves. For example, one solution involves introducing means for horizontally, (i.e. in an x, y plane) moving the lower mold half beneath the parison extrusion head in such a manner that the parison is dropped within the mold cavity. Molds which are used in typical blow molding are normally quite heavy and hence this solution requires significant effort to effectively and accurately move the mold half.
In some prior art devices, the extrusion head is moved horizontally in an x, y plane so that as the parison is extruded, it is arranged to follow and lie in the cavity in a lower mold half. Extrusion equipment used in typical blow molding is also large and heavy to support the extrusion temperatures and pressures involved and it is costly and cumbersome to move the extrusion head, even in a horizontal plane.
U.S. Pat. No. 5,030,083 to Kohno, teaches the use of a robotic hand to grasp and transport an extruded parison to a remote lower mold half having cavity and place it therein. Where a sizable parison is required, however, the swinging action of the parison induced by its movement by the robot hand can make the path the hand must follow to properly load the parison in the mold, quite complex. Another significant problem is the weight and strength of the molten parison. The parison may break under its own weight during transport from the extrusion head to the mold.
U.S. Pat. No. 5,464,635 to Geiger, discloses the use of a moveable premold having a shape matching the lower mold cavity. A molten parison is extruded into the premold which is moved under the extrusion head, by robotic or other means, to cause the parison, as it is extruded, to be deposited in to the premold cavity. Hence, once loaded with the parison, the premold is transported to the lower mold half and positioned thereover, with the premold and mold cavities substantially aligned. The premold includes openable doors or other similar acting structure so that by opening the structure, the parison is dropped directly into the mold cavity of the lower mold half. This system requires the design of a complex premold with means to accurately release the parison so that it accurately falls into the groove of the lower mold half.
In our co-pending application, we have provided an alternative solution. The alternate solution provided in our co-pending application involves the use of a relatively lightweight lower mold half the lightweight lower mold half comprises a cavity into which the parison is extruded. A robotic arm or other manipulation means is used to move the lightweight lower mold half into a suitable position so that as the parison is extruded from the extrusion head, the lower mold half may be moved so that the parison is extruded directly into place in the mold cavity. Once the extrusion process is completed, the parison is cut and the lightweight lower mold half together with the parison located therein, is then moved to a molding station. At the molding station, the lightweight lower mold half is placed in a lower mold half support. The lower mold half support provides the weight and substance as well as physical support for the lower mold half so that it may be used in a typical mold press or clamp to blow mold parts. The disclosure of our co-pending application is incorporated herein in its entirety by reference.
In accordance with this invention, a mold assembly comprises a first mold fixture. The first mold fixture includes a first mold cavity. The mold assembly includes a second mold fixture. The second mold fixture includes a second mold cavity. The first and second mold cavities define a complete mold for blow molding a parison. The first mold fixture includes drive means and the second mold fixture includes drive receiving means. The drive means of the first mold fixture and the drive receiving means of the second mold fixture are adapted to locate and lock the second mold fixture against the first mold fixture with the first and second mold cavities in registration to form the complete mold.
In accordance with another aspect of the invention, a process for blow molding parts comprises the use of a first mold fixture and a second mold fixture. The first mold fixture includes a first mold cavity and the second mold fixture includes a second mold cavity. The first and second cavities define a complete mold for blow molding a parison. The first mold fixture includes drive means and the second mold fixture includes drive receiving means. The drive means of the first mold fixture and the drive receiving means of the second mold fixture are adapted to locate and lock the second mold fixture against the first mold fixture with the first and second cavities in registration to form a complete mold. The process further comprises the steps of extruding a parison from an extrusion head. A parison is extruded from the extrusion head. While the parison is being extruded, the second mold fixture is moved so that the parison is extruded to lie within the second mold cavity. The second mold fixture is moved by manipulation means to receive the parison as it is extruded. Manipulation means are also used to translate the second mold fixture from adjacent to the extrusion head to adjacent the first mold fixture so that the second mold fixture is substantially in registry with the first mold fixture. The drive means of the first mold fixture are then extended and are received within the drive receiving means of the second mold fixture. The receipt of the drive means within the drive receiving means locates and locks the first and second mold fixtures in registry to form a complete mold. The process involves blow molding the parison within the first and second fixtures without the need for any outside clamping force.